Hemophilia B is a genetic disease caused by a deficiency of clotting factor IX. Current therapy for Hemophilia B patients is protein therapy and clinical trials are currently underway for a gene therapy approach. With the current protein therapy, a small percentage (3 percent) of patients develop inhibitory antibodies that neutralize the F.IX protein activity rendering treatment ineffective. Attempts to eliminate inhibitory antibodies by infusing high doses of F.IX or by immunosuppressive treatment are not always successful. We hypothesize that effective immune tolerance strategies will enable current therapies for Hemophilia B to be successful for all patients. In this proposal we hypothesize that Hemophilia B mice can be tolerized to FIX by oral administration of FIX. In the first aim we will determine if oral tolerance to human FIX can be achieved in neonatal or adult Hemophilia B mice. Specifically, we will generate mouse whey acidic protein promoter-human Factor IX transgenic mice and characterize the levels of hF.IX in the mouse milk. These transgenic mice will be used to determine whether ingestion of milk from the mWAP-hF.IX female mice is able to tolerize the newborn Hemophilia B mice to hF.IX. Adult Hem B mice will be fed hFIX in their water to determine if feeding the antigen to adult Hem B mice is able to induce tolerance. In the second aim we will determine if tolerance to human F.IX can be achieved by continuous expression of FIX in gut epithelium of Hemophilia B mice. This will demonstrate if adult Hem B mice can be tolerized to FiX and if continuous expression of F.IX in gut tissue may facilitate the induction of tolerance.